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From:
Martijn van Duren <openbsd+tech@list.imperialat.at>
Subject:
snmpd: move engineid into a struct
To:
tech@openbsd.org
Date:
Sun, 9 Nov 2025 12:51:34 +0100

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This diff is a bit of preparation for the next diff.
Initially I went a bit too simplistic and simply put the engineid value
and length in two separate variables inside the requiring structs. This
diff bundles the 2 variables into a struct engineid. This also helps with the
parse.y stuff.

This diff is on top of the "move smi_getticks to appl_sysuptime" diff.
It might apply without it, but not tested.

OK?

martijn@

diff c11d3fa04dc651329001615fdd8ee9886239e54a 033841d6245fb04a471b798741c0003f8568f241
commit - c11d3fa04dc651329001615fdd8ee9886239e54a
commit + 033841d6245fb04a471b798741c0003f8568f241
blob - 9eb74e5dd588d6bcd95c3f15a8571805523747e4
blob + 36cf6db636c1ce72084d983ef4688328ae9a6190
--- usr.sbin/snmpd/Makefile
+++ usr.sbin/snmpd/Makefile
@@ -4,6 +4,7 @@ PROG=		snmpd
 MAN=		snmpd.8 snmpd.conf.5
 SRCS=		mib.y parse.y log.c snmpe.c application.c application_blocklist.c \
 		    application_internal.c application_agentx.c ax.c \
+		    engine.c \
 		    trap.c smi.c snmpd.c \
 		    proc.c usm.c traphandler.c util.c
 
blob - 22b890324bfb16a0977624bc5ca1f86cad6653ce
blob + d3b17ba026afe2cb332d3ab85da99b5445e141c6
--- usr.sbin/snmpd/application_internal.c
+++ usr.sbin/snmpd/application_internal.c
@@ -530,8 +530,8 @@ struct ber_element *
 appl_internal_engine(struct ber_oid *oid)
 {
 	if (ober_oid_cmp(&OID(MIB_snmpEngineID, 0), oid) == 0)
-		return ober_add_nstring(NULL, snmpd_env->sc_engineid,
-		    snmpd_env->sc_engineid_len);
+		return ober_add_nstring(NULL, snmpd_env->sc_engineid.value,
+		    snmpd_env->sc_engineid.length);
 	else if (ober_oid_cmp(&OID(MIB_snmpEngineBoots, 0), oid) == 0)
 		return ober_add_integer(NULL, snmpd_env->sc_engine_boots);
 	else if (ober_oid_cmp(&OID(MIB_snmpEngineTime, 0), oid) == 0)
blob - /dev/null
blob + 7a6d4fe36f628994247b05825f9572c556859d9d (mode 644)
--- /dev/null
+++ usr.sbin/snmpd/engine.c
@@ -0,0 +1,35 @@
+/*	$OpenBSD$	*/
+
+/*
+ * Copyright (c) 2025 Martijn van Duren <martijn@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <string.h>
+
+#include "snmpd.h"
+
+int
+engineid_cmp(struct engineid *e1, struct engineid *e2)
+{
+	size_t min;
+	int r;
+
+	min = e1->length < e2->length ? e1->length : e2->length;
+	if ((r = memcmp(e1->value, e2->value, min)) != 0)
+		return r;
+	if (e1->length == e2->length)
+		return 0;
+	return e1->length < e2->length ? -1 : 1;
+}
blob - 3882b915ebd85bcac9b41fff40c89a9a2633c88b
blob + 555bc4050d03fd1f3b54d4ea4a745cb9fa3cfc21
--- usr.sbin/snmpd/parse.y
+++ usr.sbin/snmpd/parse.y
@@ -138,9 +138,7 @@ static size_t			 ntrapcmds = 0;
 static struct trapaddress_sym	*trapaddresses = NULL;
 static size_t			 ntrapaddresses = 0;
 
-static uint8_t			 engineid[SNMPD_MAXENGINEIDLEN];
 static int32_t			 enginepen;
-static size_t			 engineidlen;
 
 static unsigned char		 sha256[SHA256_DIGEST_LENGTH];
 
@@ -165,6 +163,7 @@ typedef struct {
 		}		 data;
 		enum usmauth	 auth;
 		enum usmpriv	 enc;
+		struct engineid	 engineid;
 	} v;
 	int lineno;
 } YYSTYPE;
@@ -197,6 +196,7 @@ typedef struct {
 %type	<v.auth>	auth
 %type	<v.enc>		enc
 %type	<v.ax>		agentxopts agentxopt
+%type	<v.engineid>	engineid_local enginefmt_local enginefmt
 
 %%
 
@@ -308,12 +308,11 @@ main		: LISTEN ON listen_udptcp
 			    axm_entry);
 		}
 		| engineid_local {
-			if (conf->sc_engineid_len != 0) {
+			if (conf->sc_engineid.length != 0) {
 				yyerror("Redefinition of engineid");
 				YYERROR;
 			}
-			memcpy(conf->sc_engineid, engineid, engineidlen);
-			conf->sc_engineid_len = engineidlen;
+			conf->sc_engineid = $1;
 		}
 		| READONLY COMMUNITY STRING	{
 			if (strlcpy(conf->sc_rdcommunity, $3,
@@ -593,46 +592,50 @@ agentxopts	: /* empty */			{
 		;
 
 enginefmt	: IP4 STRING			{
-			struct in_addr addr;
+			in_addr_t addr;
 
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_IPv4;
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_IPv4;
 			if (inet_pton(AF_INET, $2, &addr) != 1) {
 				yyerror("Invalid ipv4 address: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			memcpy(engineid + engineidlen, &addr,
-			    sizeof(engineid) - engineidlen);
-			engineid[0] |= SNMP_ENGINEID_NEW;
-			engineidlen += sizeof(addr);
+			memcpy($$.value + $$.length, &addr, sizeof(addr));
+			$$.length += sizeof(addr);
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| IP6 STRING			{
-			struct in6_addr addr;
+			uint8_t addr[16];
 
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_IPv6;
-			if (inet_pton(AF_INET6, $2, &addr) != 1) {
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_IPv6;
+			if (inet_pton(AF_INET6, $2, addr) != 1) {
 				yyerror("Invalid ipv6 address: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			memcpy(engineid + engineidlen, &addr,
-			    sizeof(engineid) - engineidlen);
-			engineid[0] |= SNMP_ENGINEID_NEW;
-			engineidlen += sizeof(addr);
+			memcpy($$.value + $$.length, addr, sizeof(addr));
+			$$.length += sizeof(addr);
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| MAC STRING			{
 			size_t i;
 
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_MAC;
 			if (strlen($2) != 5 * 3 + 2) {
 				yyerror("Invalid mac address: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_MAC;
 			for (i = 0; i < 6; i++) {
-				if (fromhexstr(engineid + engineidlen + i,
+				if (fromhexstr($$.value + $$.length + i,
 				    $2 + (i * 3), 2) == NULL ||
 				    $2[i * 3 + 2] != (i < 5 ? ':' : '\0')) {
 					yyerror("Invalid mac address: %s", $2);
@@ -640,108 +643,119 @@ enginefmt	: IP4 STRING			{
 					YYERROR;
 				}
 			}
-			engineid[0] |= SNMP_ENGINEID_NEW;
-			engineidlen += 6;
+			$$.length += 6;
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| TEXT STRING			{
-			size_t i, fmtstart;
+			size_t i;
 
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_TEXT;
-			for (i = 0, fmtstart = engineidlen;
-			    i < sizeof(engineid) - engineidlen && $2[i] != '\0';
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_TEXT;
+			for (i = 0;
+			    $$.length < sizeof($$.value) && $2[i] != '\0';
 			    i++) {
 				if (!isprint($2[i])) {
 					yyerror("invalid text character");
 					free($2);
 					YYERROR;
 				}
-				engineid[fmtstart + i] = $2[i];
-				engineidlen++;
+				$$.value[$$.length++] = $2[i];
 			}
 			if (i == 0 || $2[i] != '\0') {
 				yyerror("Invalid text length: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			engineid[0] |= SNMP_ENGINEID_NEW;
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| OCTETS STRING			{
-			if (strlen($2) / 2 > sizeof(engineid) - 1) {
-				yyerror("Invalid octets length: %s", $2);
-				free($2);
-				YYERROR;
-			}
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_OCT;
 
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_OCT;
-			if (fromhexstr(engineid + engineidlen, $2,
+			if (strlen($2) / 2 > sizeof($$.value) - $$.length) {
+				yyerror("Invalid octets length: %s", $2);
+				free($2);
+				YYERROR;
+			}
+			if (fromhexstr($$.value + $$.length, $2,
 			    strlen($2)) == NULL) {
 				yyerror("Invalid octets: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			engineidlen += strlen($2) / 2;
-			engineid[0] |= SNMP_ENGINEID_NEW;
+			$$.length += strlen($2) / 2;
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| AGENTID STRING		{
+			$$ = (struct engineid){};
+			$$.length = 4;
+
 			if (strlen($2) / 2 != 8) {
 				yyerror("Invalid agentid length: %s", $2);
 				free($2);
 				YYERROR;
 			}
-
-			if (fromhexstr(engineid + engineidlen, $2,
+			if (fromhexstr($$.value + $$.length, $2,
 			    strlen($2)) == NULL) {
 				yyerror("Invalid agentid: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			engineidlen += 8;
-			engineid[0] |= SNMP_ENGINEID_OLD;
+			$$.length += 8;
+			$$.value[0] |= SNMP_ENGINEID_OLD;
 			free($2);
 		}
 		| HOSTHASH STRING		{
+			$$ = (struct engineid){};
+			$$.length = 4;
+
 			if (enginepen != PEN_OPENBSD) {
 				yyerror("hosthash only allowed for pen "
 				    "openbsd");
 				YYERROR;
 			}
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_HH;
-			memcpy(engineid + engineidlen,
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_HH;
+			memcpy($$.value + $$.length,
 			    SHA256($2, strlen($2), sha256),
-			    sizeof(engineid) - engineidlen);
-			engineidlen = sizeof(engineid);
-			engineid[0] |= SNMP_ENGINEID_NEW;
+			    sizeof($$.value) - $$.length);
+			$$.length = sizeof($$.value);
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		| NUMBER STRING			{
+			$$ = (struct engineid){};
+			$$.length = 4;
+
 			if (enginepen == PEN_OPENBSD) {
 				yyerror("%lld is only allowed when pen is not "
 				    "openbsd", $1);
 				YYERROR;
 			}
-
 			if ($1 < 128 || $1 > 255) {
 				yyerror("Invalid format number: %lld\n", $1);
 				YYERROR;
 			}
-			if (strlen($2) / 2 > sizeof(engineid) - 1) {
+			$$.value[$$.length++] = (uint8_t)$1;
+
+			if (strlen($2) / 2 > sizeof($$.value) - $$.length) {
 				yyerror("Invalid octets length: %s", $2);
 				free($2);
 				YYERROR;
 			}
 
-			engineid[engineidlen++] = (uint8_t)$1;
-			if (fromhexstr(engineid + engineidlen, $2,
+			if (fromhexstr($$.value + $$.length, $2,
 			    strlen($2)) == NULL) {
 				yyerror("Invalid octets: %s", $2);
 				free($2);
 				YYERROR;
 			}
-			engineidlen += strlen($2) / 2;
-			engineid[0] |= SNMP_ENGINEID_NEW;
+			$$.length += strlen($2) / 2;
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 			free($2);
 		}
 		;
@@ -761,12 +775,14 @@ enginefmt_local	: enginefmt
 				YYERROR;
 			}
 
-			engineid[engineidlen++] = SNMP_ENGINEID_FMT_HH;
-			memcpy(engineid + engineidlen,
+			$$ = (struct engineid){};
+			$$.length = 4;
+			$$.value[$$.length++] = SNMP_ENGINEID_FMT_HH;
+			memcpy($$.value + $$.length,
 			    SHA256(hostname, strlen(hostname), sha256),
-			    sizeof(engineid) - engineidlen);
-			engineidlen = sizeof(engineid);
-			engineid[0] |= SNMP_ENGINEID_NEW;
+			    sizeof($$.value) - $$.length);
+			$$.length = sizeof($$.value);
+			$$.value[0] |= SNMP_ENGINEID_NEW;
 		}
 		;
 
@@ -792,9 +808,14 @@ pen		: /* empty */			{
 engineid_local	: ENGINEID pen			{
 			uint32_t npen = htonl(enginepen);
 
-			memcpy(engineid, &npen, sizeof(enginepen));
-			engineidlen = sizeof(enginepen);
-		} enginefmt_local
+			memcpy($$.value, &npen, sizeof(npen));
+			$$.length = sizeof(npen);
+		} enginefmt_local {
+			$$.value[0] |= $4.value[0] & SNMP_ENGINEID_NEW;
+			memcpy($$.value + $$.length, $4.value + $$.length,
+			    $4.length - $$.length);
+			$$.length = $4.length;
+		}
 
 system		: SYSTEM sysmib
 		;
@@ -1854,18 +1875,18 @@ parse_config(const char *filename, u_int flags)
 
 
 	/* Must be identical to enginefmt_local:HOSTHASH */
-	if (conf->sc_engineid_len == 0) {
+	if (conf->sc_engineid.length == 0) {
 		if (gethostname(hostname, sizeof(hostname)) == -1)
 			fatal("gethostname");
-		memcpy(conf->sc_engineid, &npen, sizeof(npen));
-		conf->sc_engineid_len += sizeof(npen);
-		conf->sc_engineid[conf->sc_engineid_len++] |=
+		memcpy(conf->sc_engineid.value, &npen, sizeof(npen));
+		conf->sc_engineid.length += sizeof(npen);
+		conf->sc_engineid.value[conf->sc_engineid.length++] =
 		    SNMP_ENGINEID_FMT_HH;
-		memcpy(conf->sc_engineid + conf->sc_engineid_len,
+		memcpy(conf->sc_engineid.value + conf->sc_engineid.length,
 		    SHA256(hostname, strlen(hostname), sha256),
-		    sizeof(conf->sc_engineid) - conf->sc_engineid_len);
-		conf->sc_engineid_len = sizeof(conf->sc_engineid);
-		conf->sc_engineid[0] |= SNMP_ENGINEID_NEW;
+		    sizeof(conf->sc_engineid.value) - conf->sc_engineid.length);
+		conf->sc_engineid.length = sizeof(conf->sc_engineid.value);
+		conf->sc_engineid.value[0] |= SNMP_ENGINEID_NEW;
 	}
 
 	/* Setup default listen addresses */
blob - 44773fae763979f619296a7421a8ea87e7429a46
blob + 5fefd671b71a9cea26758de538109e8e871cb2e1
--- usr.sbin/snmpd/snmpd.h
+++ usr.sbin/snmpd/snmpd.h
@@ -179,6 +179,11 @@ struct privsep_fd {
  * daemon structures
  */
 
+struct engineid {
+	uint8_t			 value[SNMPD_MAXENGINEIDLEN];
+	size_t			 length;
+};
+
 #define MSG_HAS_AUTH(m)		(((m)->sm_flags & SNMP_MSGFLAG_AUTH) != 0)
 #define MSG_HAS_PRIV(m)		(((m)->sm_flags & SNMP_MSGFLAG_PRIV) != 0)
 #define MSG_SECLEVEL(m)		((m)->sm_flags & SNMP_MSGFLAG_SECMASK)
@@ -219,8 +224,7 @@ struct snmp_message {
 	long long		 sm_secmodel;
 	u_int32_t		 sm_engine_boots;
 	u_int32_t		 sm_engine_time;
-	uint8_t			 sm_ctxengineid[SNMPD_MAXENGINEIDLEN];
-	size_t			 sm_ctxengineid_len;
+	struct engineid		 sm_ctxengineid;
 	char			 sm_ctxname[SNMPD_MAXCONTEXNAMELEN+1];
 
 	/* USM */
@@ -407,8 +411,7 @@ struct snmpd {
 	char			 sc_rwcommunity[SNMPD_MAXCOMMUNITYLEN];
 	char			 sc_trcommunity[SNMPD_MAXCOMMUNITYLEN];
 
-	uint8_t			 sc_engineid[SNMPD_MAXENGINEIDLEN];
-	size_t			 sc_engineid_len;
+	struct engineid		 sc_engineid;
 
 	struct snmp_stats	 sc_stats;
 	struct snmp_system	 sc_system;
@@ -444,6 +447,9 @@ extern struct snmpd *snmpd_env;
 struct snmpd	*parse_config(const char *, u_int);
 int		 cmdline_symset(char *);
 
+/* engine.c */
+int		 engineid_cmp(struct engineid *, struct engineid *);
+
 /* snmpe.c */
 void		 snmpe(struct privsep *, struct privsep_proc *);
 void		 snmpe_shutdown(void);
blob - d444c8d9b8a47d7da9242e9372d1b88241dece5b
blob + 67dcfc523ad4171ad87ab71a2c21aca7cc639187
--- usr.sbin/snmpd/snmpe.c
+++ usr.sbin/snmpd/snmpe.c
@@ -114,7 +114,7 @@ snmpe_init(struct privsep *ps, struct privsep_proc *p,
 		fatal("pledge");
 
 	log_info("snmpe %s: ready",
-	    tohexstr(env->sc_engineid, env->sc_engineid_len));
+	    tohexstr(env->sc_engineid.value, env->sc_engineid.length));
 	trap_init();
 }
 
@@ -305,12 +305,14 @@ snmpe_parse(struct snmp_message *msg)
 		}
 
 		if (ober_scanf_elements(a, "{xxeS$}$",
-		    &engineid, &msg->sm_ctxengineid_len, &ctxname, &len,
+		    &engineid, &msg->sm_ctxengineid.length, &ctxname, &len,
 		    &msg->sm_pdu) != 0)
 			goto parsefail;
-		if (msg->sm_ctxengineid_len > sizeof(msg->sm_ctxengineid))
+		if (msg->sm_ctxengineid.length >
+		    sizeof(msg->sm_ctxengineid.value))
 			goto parsefail;
-		memcpy(msg->sm_ctxengineid, engineid, msg->sm_ctxengineid_len);
+		memcpy(msg->sm_ctxengineid.value, engineid,
+		    msg->sm_ctxengineid.length);
 		if (len > SNMPD_MAXCONTEXNAMELEN)
 			goto parsefail;
 		memcpy(msg->sm_ctxname, ctxname, len);
@@ -456,7 +458,7 @@ badversion:
 		    "request %lld", __func__, msg->sm_host, msg->sm_port,
 		    snmpe_pdutype2string(msg->sm_pdutype), msg->sm_flags,
 		    msg->sm_secmodel, msg->sm_username,
-		    tohexstr(msg->sm_ctxengineid, msg->sm_ctxengineid_len),
+		    tohexstr(msg->sm_ctxengineid.value, msg->sm_ctxengineid.length),
 		    msg->sm_ctxname, msg->sm_request);
 	else
 		log_debug("%s: %s:%hd: SNMPv%d '%s' pdutype %s request %lld",
@@ -849,7 +851,7 @@ snmpe_encode(struct snmp_message *msg)
 	pdu = epdu = ober_add_sequence(NULL);
 	if (msg->sm_version == SNMP_V3) {
 		if ((epdu = ober_printf_elements(epdu, "xs{",
-		    snmpd_env->sc_engineid, snmpd_env->sc_engineid_len,
+		    snmpd_env->sc_engineid.value, snmpd_env->sc_engineid.length,
 		    msg->sm_ctxname)) == NULL) {
 			ober_free_elements(pdu);
 			return -1;
blob - f676ead16b9622eea34346322e562365ec058815
blob + 11446e02974afa4f87a43e7a8454f110a749b015
--- usr.sbin/snmpd/trap.c
+++ usr.sbin/snmpd/trap.c
@@ -109,10 +109,7 @@ trap_send(struct ber_oid *oid, struct ber_element *elm
 			msg->sm_secmodel = SNMP_SEC_USM;
 			msg->sm_engine_time = snmpd_engine_time();
 			msg->sm_engine_boots = snmpd_env->sc_engine_boots;
-			memcpy(msg->sm_ctxengineid, snmpd_env->sc_engineid,
-			    snmpd_env->sc_engineid_len);
-			msg->sm_ctxengineid_len =
-			    snmpd_env->sc_engineid_len;
+			msg->sm_ctxengineid = snmpd_env->sc_engineid;
 			(void)strlcpy(msg->sm_username, tr->ta_usmusername,
 			    sizeof(msg->sm_username));
 			msg->sm_user = tr->ta_usmuser;
blob - 93324b557a9aadfe6acc42c94ea2b1397bc4475a
blob + b38eaa9d4b02a389eae9ea5f7c8808e4c32cf9e5
--- usr.sbin/snmpd/usm.c
+++ usr.sbin/snmpd/usm.c
@@ -266,10 +266,11 @@ usm_decode(struct snmp_message *msg, struct ber_elemen
 	off_t			 offs, offs2;
 	char			*usmparams;
 	size_t			 len;
-	size_t			 enginelen, userlen, digestlen, saltlen;
+	size_t			 userlen, digestlen, saltlen;
 	struct ber		 ber;
 	struct ber_element	*usm = NULL, *next = NULL, *decr;
-	char			*engineid;
+	struct engineid		 engineid;
+	char			*engineidv;
 	char			*user;
 	char			*digest, *salt;
 	u_long			 now;
@@ -297,7 +298,7 @@ usm_decode(struct snmp_message *msg, struct ber_elemen
 	smi_debug_elements(usm);
 #endif
 
-	if (ober_scanf_elements(usm, "{xiixpxx$", &engineid, &enginelen,
+	if (ober_scanf_elements(usm, "{xiixpxx$", &engineidv, &engineid.length,
 	    &engine_boots, &engine_time, &user, &userlen, &offs2,
 	    &digest, &digestlen, &salt, &saltlen) != 0) {
 		*errp = "cannot decode USM params";
@@ -306,10 +307,10 @@ usm_decode(struct snmp_message *msg, struct ber_elemen
 	}
 
 	log_debug("USM: engineid '%s', engine boots %lld, engine time %lld, "
-	    "user '%s'", tohexstr(engineid, enginelen), engine_boots,
+	    "user '%s'", tohexstr(engineidv, engineid.length), engine_boots,
 	    engine_time, user);
 
-	if (enginelen > SNMPD_MAXENGINEIDLEN ||
+	if (engineid.length > sizeof(engineid.value) ||
 	    userlen > SNMPD_MAXUSERNAMELEN ||
 	    !usm_valid_digestlen(digestlen) ||
 	    (saltlen != (MSG_HAS_PRIV(msg) ? SNMP_USM_SALTLEN : 0))) {
@@ -318,8 +319,8 @@ usm_decode(struct snmp_message *msg, struct ber_elemen
 		goto done;
 	}
 
-	if (enginelen != snmpd_env->sc_engineid_len ||
-	    memcmp(engineid, snmpd_env->sc_engineid, enginelen) != 0) {
+	memcpy(engineid.value, engineidv, engineid.length);
+	if (engineid_cmp(&snmpd_env->sc_engineid, &engineid) != 0) {
 		*errp = "unknown engine id";
 		msg->sm_usmerr = OIDVAL_usmErrEngineId;
 		stats->snmp_usmnosuchengine++;
@@ -436,7 +437,7 @@ usm_encode(struct snmp_message *msg, struct ber_elemen
 	msg->sm_engine_boots = (u_int32_t)snmpd_env->sc_engine_boots;
 	msg->sm_engine_time = (u_int32_t)snmpd_engine_time();
 	if ((a = ober_printf_elements(usm, "xdds",
-	    snmpd_env->sc_engineid, snmpd_env->sc_engineid_len,
+	    snmpd_env->sc_engineid.value, snmpd_env->sc_engineid.length,
 	    msg->sm_engine_boots, msg->sm_engine_time,
 	    msg->sm_username)) == NULL)
 		goto done;
@@ -720,13 +721,13 @@ usm_passwd2key(const EVP_MD *md, char *passwd, int *ma
 	assert(snmpd_env->sc_engineid_len <= SNMPD_MAXENGINEIDLEN);
 #endif
 	memcpy(pwbuf, keybuf, dlen);
-	memcpy(pwbuf + dlen, snmpd_env->sc_engineid,
-	    snmpd_env->sc_engineid_len);
-	memcpy(pwbuf + dlen + snmpd_env->sc_engineid_len, keybuf, dlen);
+	memcpy(pwbuf + dlen, snmpd_env->sc_engineid.value,
+	    snmpd_env->sc_engineid.length);
+	memcpy(pwbuf + dlen + snmpd_env->sc_engineid.length, keybuf, dlen);
 
 	if (!EVP_DigestInit_ex(ctx, md, NULL) ||
 	    !EVP_DigestUpdate(ctx, pwbuf,
-	    2 * dlen + snmpd_env->sc_engineid_len) ||
+	    2 * dlen + snmpd_env->sc_engineid.length) ||
 	    !EVP_DigestFinal_ex(ctx, keybuf, &dlen)) {
 		EVP_MD_CTX_free(ctx);
 		return NULL;